I have a question. Can the Pikachu-colored Pichu be obtained from anywhere outside of Japan? If not, that's a whole in-game event in HG/SS that the rest of the world cannot obtain.
As of right now, the Pikachu Colored Pichu was obtained in the 12th movie event in Japan. However, because of capability with Wi-Fi, there are certain people here trading legit Pikachu Colored Pichus. As for it being held as an event outside of Japan, I wouldn't expect that until the 12th movie comes out in each country for others to obtain the event for the Pichu on their own.
More than likely, it will be held outside of Japan, and at least in the US it will for the most part as well. I'm sure this won't be an exclusive Japan only event as the Gizamimi Pichu [Notched Ear] is quite special for the remakes and I don't think Game Freak will risk the loss in money for this, when they can earn more by holding up the event outside.